The MTC User Equipment (MTC UE) is also known as an M2M user communication device and is the main application form of the Internet of things at this stage. Smart metering is one of the most typical applications of the MTC device, and most of smart metering type MTC devices are all fixedly installed in environments with low coverage performance such as a basement and so on. In order to ensure that such type of MTC devices can maintain a normal communication with the base station system, usually it is required to deploy additional devices such as sites and relays and so on, which will undoubtedly greatly increase the deployment cost of the carriers. To this end, companies such as Vodafone raised the needs for improving/enhancing the coverage of each physical channel of the smart metering type MTC devices on the premise of without increasing additional device deployments in the technical proposal RP-121282 in the 3GPP RAN.
The Radio Frame (RF) in the LTE system includes frame structures of the Frequency Division Duplex (referred to as FDD) mode and the Time Division Duplex (referred to as TDD) mode.
FIG. 1 is a schematic diagram of the frame structure of the FDD mode in the LTE technology according to the related art, as shown in FIG. 1, a 10 millisecond (ms) radio frame consists of twenty slots whose length is 0.5 ms each and which are numbered 0 to 19, and slots 2i and 2i+1 form a subframe i whose length is 1 ms.
FIG. 2 is a schematic diagram of the frame structure of the TDD mode in the LTE technology according to the related art, as shown in FIG. 2, a 10 ms radio frame consists of two 5 ms half frames, and one half frame includes five subframes whose length is 1 ms each, and the subframe i is defined as the slot 2i and the slot 2i+1 whose length is 0.5 ms each.
In the abovementioned two frame structures, for the Normal Cyclic Prefix (referred to as Normal CP), one slot contains 7 symbols whose length is 66.7 microseconds (us) each, wherein, the CP length of the first symbol is 5.21 us, and the CP length of each of the other six symbols is 4.69 us; for the Extended Cyclic Prefix (referred to as Extended CP), one slot contains six symbols, and the CP length of each of the symbols can be 16.67 us.
FIG. 3 is a schematic diagram of the time-frequency structure of various physical channels of the common downlink subframe in the LTE according to the related art, as shown in FIG. 3, the following several downlink physical channels are defined in the LTE: a Physical Control Format Indicator Channel (PCFICH), a Physical Hybrid Automatic Retransmission Request Indicator Channel (PHICH), a Physical Downlink Control Channel (PDCCH), and a Physical Downlink Shared Channel (PDSCH).
Wherein, when the downlink subframe does not have the PDCCH, there is no need to transmit the PCFICH. When the control format indicator CFI value is greater than 0, the PCFICH needs to be transmitted in the subframe and is located in the first symbol of the downlink subframe, which is used to indicate the number of OFDM symbols occupied by the PDCCH control signaling in one subframe. The set of OFDM symbols that can be used for PDCCH transmission in one subframe is as shown in Table 1.
TABLE 1the number of OFDM symbols used for the PDCCHThe numberof OFDMThe number ofsymbols (CFIOFDMvalue) usedsymbols (CFIfor thevalue) used forPDCCH whenthe PDCCHSubframeNRBDL >10when NRBDL ≦10For one or two cell-specific1, 22antenna ports, MBSFN subframesin the carrier supporting both thePMCH transmission and PDSCHtransmissionFor four cell-specific antenna22ports, MBSFN subframes in thecarrier supporting both the PMCHtransmission and PDSCHtransmissionMBSFN subframes in the carrier not00supporting the PDSCH transmissionOther cases1, 2, 32, 3, 4
The PHICH is located in the first symbol or the first three symbols of the subframe, and it is used to carry the ACK/NACK feedback information of the uplink PUSCH.
The PDCCH is used to bear Downlink Control Information (referred to as DCI), including: uplink and downlink scheduling information, as well as uplink power control information. The time-domain position starts from the first symbol of the downlink subframe, and the number of symbols occupied is indicated by the PCFICH, and the frequency domain position is mapped to all system bandwidths.
The PDSCH is used to transmit system public messages, paging messages and downlink data, the frequency domain position of the PDSCH in the subframe is indicated by the PDCCH, and its time-domain position starts from the next OFDM symbol in the control area and until the subframe ends. Thus, knowing the number of PDCCH symbols is equivalent to knowing the time domain starting symbol position of the PDSCH in the same subframe.
The content of the control information transmitted in the enhanced PDCCH (referred to as ePDCCH) is the same as that of the original PDCCH, but it is located within the PDSCH area, and its time-domain starting position is the same as that of the PDSCH.
Generally, the order of a terminal receiving downlink subframes is as shown in FIG. 4, first the PBCH is received to obtain information such as the system bandwidth, then the PCFICH is decoded to obtain the CFI information, i.e. information of the number of symbols occupied by the PDCCH and information of the time-domain starting position of the PDSCH, and then the PDCCH is blindly detected in the corresponding subframe area to obtain the DCI, then the PDSCH at the corresponding time-frequency position is decoded according to the indication of the DCI signaling to obtain the downlink data.
In the RAN #60 plenary meeting, the proposal RP-130848 of Vodafone proposed the technical requirements that, for the coverage enhanced MTC UE, functions of a plurality of physical channels can be simplified or be replaced with other channels or mechanisms to be achieved, for example, the PCFICH can be avoided, and functions of the PCFICH are achieved through other solutions. Therefore, on the one hand, the downlink physical channel structure of the coverage enhanced MTC UE can be simplified and continuous decoding errors can be avoided, on the other hand, the consideration of the PCFICH coverage enhancement is also saved, and the coverage enhanced MTC UE will not be limited by the physical channel. But if the channel is removed directly and a corresponding avoidance policy is not given, the complexity of blindly detecting the PDCCH (ePDCCH) will be significantly increased.
Therefore, for the PCFICH channel of the coverage enhanced MTC UE, an alternative avoidance policy must be designed, which not only will not affect the downlink subframe reception of the non-coverage enhanced normal UE, but also needs to ensure that the coverage enhanced MTC terminal still can know the number of symbols occupied by the PDCCH in each downlink subframe or the time-domain starting position of the PDSCH even without decoding the CFICH, thus completing a correct reception of the downlink data.
With respect to the problem of PCFICH avoidance or function substitutions, currently no effective solutions have been put forward.